This section provides background information related to the present disclosure which is not necessarily prior art.
Various technological solutions are known for generative production processes in which a three-dimensional object is produced layer by layer by means of sintering or melting a powdery base material. Plastic powders which can easily be processed due to their low melting points and low heat conductivity are often used as the raw material.
Typical processes in this context are selective laser sintering (SLS), stereolithography (STL), and fused deposition modeling (FDM). In selective laser sintering, for example, a 3D CAD file is divided into two-dimensional planes having a thickness of about 0.1 mm. The coordinates of these planes are transmitted as datasets to a control computer. Then initially one layer of the powdery raw material is applied to the construction platform. Such materials already are the subject matter of numerous property rights. DE 197 47 309 B4, for example, describes a polyamide powder which is designed for selective laser sintering. The surface of the powder applied to the construction platform is then irradiated with a laser in accordance with the coordinates of the first plane. This energy input sinters the powder irradiated with the laser, such that a firm structure is formed. After completion of processing in this first plane, the construction platform is lowered by the layer thickness of one plane, and a new powder layer is applied. These steps are repeated in accordance with the number of planes, whereby a three-dimensional object is built layer by layer.
As the processing advances from plane to plane, powdery material remains outside the areas covered by the laser. This powder surrounds the three-dimensional object being built and initially provides some support during the further processing. However, this powder also remains after the three-dimensional object has been completely built and is removed from the platform.
It therefore seems obvious to use this unsolidified material, typically called “waste powder”, for building another three-dimensional object. However, this can only be done depending on conditions, since at least the portions of waste powder disposed near the built object have been subjected to temperatures slightly below the melting point in the previous processing operations. This thermal stress inevitably leads to an aging process, as a result of which the original properties of the powdery raw material change somewhat in most cases. Consequently, waste powder is not used as the sole raw material but is always mixed with new powder.
DE 103 30 590 A1 says in this context that the portion of waste powder can be increased if a mixture of waste powder and new powder comprises a polyamide in which the ratio of terminal carboxyl groups to terminal amino groups is at least 2:1.
EP 2 368 696 B1 describes a powder mixture of two polyamide 12 powders, each of which comprise differing increases in viscosity numbers and are intermixed at a ratio between 10 and 30 percent by weight.
The references regarding prior state of the art cited herein primarily relate to compositions of waste powder and new powder that are chemically adjusted to one another. However, tests have shown that such chemical adjustment of the components alone is at least in some use cases not sufficient to achieve a high-quality base material for use in generative production processes by mixing waste powder and new powder. It is apparent that further treatment steps are useful, but hardly any exact information is known in this respect from the relevant technical literature.